The present invention relates to high-speed integrated circuit output/input signaling, and more particularly to a low-power pulse signaling (LPPS) circuit.
A variety of electronic systems rely on improvements in high-speed signaling to increase performance. Networks can operate at higher data rates when signals are propagated more quickly between stations and within network switches. Telephone systems can handle more calls when faster transmission occurs. At high data rates, the media through which signals are transmitted on a printed circuit board or within integrated circuit packages has characteristics similar to the transmission media in the aforementioned systems. Thus, constant improvements to signaling at this level are also necessary.
An example of a conventional circuit approach to high-speed signaling is low-voltage differential signaling (LVDS). This approach is described in more detail in J. Goldie and G. Nicholson, “A case for low voltage differential signaling as the ubiquitous interconnect technology,” Electronic Systems, March 1999, pp. 39–50, and is herein incorporated by reference. In general, this type of driver employs a differential output signal representing a logic “0” or “1” to drive a dual transmission line. However, with LVDS the differential output constantly remains in a logic state, thus drawing considerable DC power. For example, a dual transmission line employing LVDS is typically terminated with a 100 ohm resistor with a differential voltage of 0.35 V across it. This results in a DC current of 3.5 mA through the resistor, regardless of the logic state of the differential output. Furthermore, additional output buffer circuitry can add to the DC current draw of a system employing LVDS.
Another example of an existing signaling system is HyperTransport I/O, which is described in more detail in “HyperTransport I/O Link Specification, Revision 1-03, Oct. 10, 2001,” and is herein incorporated by reference. HyperTransport is similar to LVDS, but HyperTransport has a lower supply voltage and a nominal differential output voltage of 0.6 V, rather than the 0.35 V across a 100 ohm resistor seen in LVDS. Like LVDS, HyperTransport also has a DC current through the output resistor whether the output is a logic “0” or a logic “1”
Another common signaling system employs emitter-coupled logic (ECL). In a typical configuration, an ECL output driver drives a current of about 22 mA when the output is high and about 4 mA when the output is low. Thus, power is continuously dissipated regardless of the logic state of the output of the driver.
There is a need for a high-speed signaling circuit approach that eliminates the continuous power dissipation which occurs in conventional high-speed signaling systems.